Locking device of a motor vehicle for securing a displaceable motor vehicle component

ABSTRACT

A locking device for securing a motor vehicle component which is displaceable relative to a motor vehicle structure and which may be secured by means of the locking device within a displacement range in a respective position of rest reached by displacement is provided. The locking device comprising at least one first frictional element and at least one second frictional element, which is moved relative to the first frictional element upon displacement of the motor vehicle component and thereby may slide with a friction surface along a friction surface of the first frictional element under sliding friction conditions and which, in a respective position of rest of the motor vehicle component, with its friction surface bears against the friction surface of the second frictional element under static friction conditions. A flowable additional medium is provided which may be brought, upon a relative movement of the frictional elements, between their friction surfaces.

CROSS-REFERENCE TO A RELATED APPLICATION

This application is a National Phase Patent Application of InternationalPatent Application Number PCT/EP2008/058928, filed on Jul. 9, 2008,which claims priority of German Utility Model Application Number 20 2007009 824.3, filed on Jul. 10, 2007.

BACKGROUND

The invention relates to a locking device of a motor vehicle forsecuring a displaceable, in particular swivelling or hinged or moveable,vehicle component which is displaceable with respect to a structuralassembly of a motor vehicle and which may be continuously secured in arespective displaced state by means of the locking device.

Such a locking device comprises a first structural frictional element aswell as a second frictional element associated to the displaceable motorvehicle component which second frictional element, upon displacement ofthe motor vehicle component, is moved relative to the first frictionalelement and thereby, under sliding friction conditions, with a frictionsurface slides along a friction surface of the first frictional elementand which, in a position of rest of the displaced motor vehiclecomponent, and under static friction conditions, with its frictionsurface frictionally bears against the friction surface of the firstfrictional element.

The capability of the displaceable motor vehicle component of beingcontinuously lockable by means of the associated locking device therebyhas not to be necessarily provided in the entire, at most possibleadjustment range of the respective motor vehicle component. Thus, itcould be quite sufficient if—depending on the specific application—adisplaceable motor vehicle component may be merely secured in a partialrange of the maximum adjustment range in a respective displaced positionby means of the locking device. The range in which the locking device iseffective is here also described as displacement range.

The motor vehicle component, which may be continuously secured in adisplaced state, may for example be a motor vehicle door (e.g., a sideor rear door) or a closing flap (e.g., a front flap or tailgate) of amotor vehicle which can be hinged away from a motor vehicle structure,for example in order to provide access to a vehicle interior in the caseof a motor vehicle door or access to a vehicle motor or a trunk in thecase of a closing flap. In this context, it may be desired to not swivelthe respective motor vehicle component to a maximum possible swivelposition, but only to carry out a limited swivelling into a partiallyopened position with a swivel angle being smaller than in a completelyopened position. This may be for example then important if other carsare parked in the vicinity of a motor vehicle, which other cars shallnot be damaged upon swivelling of a motor vehicle component. Then, it isnecessary to allow the respective motor vehicle component to be securedin its partially swivelled position in such a way that it is notswivelled further just due to a gust of wind or due to a unintentionalcontact, which could just cause a collision with the adjoining vehicle.For this reason so-called locking devices at motor vehicles are known,cf. DE 10 2004 034 247 B3.

In this context, it is important that such a locking device ensures atthe one hand a sufficient smooth movability of a displaceable motorvehicle component, such as a vehicle door, upon opening or closing, buton the other hand secures the respective motor vehicle component in arespective displaced state so reliably that even stronger gusts of windor such the like do not cause a further displacement.

SUMMARY

The problem underlying the invention is hence to improve a lockingdevice of the initially stated type with regard to the ease of operationand at the same time a reliable securing of a displaceable motor vehiclecomponent.

According to an exemplary embodiment of the invention, a flowableadditional medium is associated to the friction surfaces of the twofrictional elements, which additional medium may be, upon a movement ofthe second frictional element with its friction surface along thefriction surface of the first frictional element, between said frictionsurfaces in order to reduce the sliding friction, in particular in sucha manner, that the ratio of the static friction to the sliding frictionis substantially increased compared to a dry operation of thearrangement without an additional medium.

During a relative movement of the second frictional element with respectto the first frictional element which is caused by the displacement ofthe motor vehicle component, flowable additional medium may beaccommodated between the friction surfaces of the frictional elements,which friction surfaces facing each other and which frictional elementsbeing associated to one other, channels are provided on at least one ofthe frictional elements, in particular on the moveable second frictionalelement, which channels for example may be formed by recessed structuresof the frictional element. For this purpose, a friction surface of africtional element may consist of a plurality of spherical sections,which form channels at the places at which they respectively meet.Furthermore, a type of pimpled surface structure of a frictional elementand/or grooves, flutes or the like, which extend along a direction ofbracing of the frictional elements, and/or grooves, flutes or the like,which in the manner of a screw circumferentially extend, may be providedat the frictional element, and so on.

As friction parings which may be used for the friction surfaces of thetwo frictional elements, which friction surfaces cooperate with eachother, particularly also in combination with an additional orintermediate medium, for example steel for the one and a plastic for theother friction surface or light metal casting on the one hand/plastic onthe other hand or plastic/plastic or steel/light metal casting aresuitable. Polyamide (PA), polyurethane (PU), polystyrene (PS),polycarbonate (PC), polyoxymethylene (POM), polysulfone (PSU),poly-2,6-dimethyl-1,4-phenylester (PPE), poletheretherketone (PEEK) andacrylic butadiene styrene (ABS) have been thereby principally proven inexperiments to be suitable plastics.

As additional or intermediate medium, oil, in particular oils which donot interfere with the plastic or synthetic material used for a frictionsurface by etching, swelling or the like, as well as emulsions anddispersions based on oil and further paste-like lubricants, such asgrease, are suitable. A specific example for an additional medium isflour silicone basis oil with ester additives.

The additional or intermediate medium is thereby advantageously housedin a housing which—as further described below—further serves for the atleast two frictional elements, wherein in particular frictional elementsmay also be provided which are fixed to the housing.

Using a paste-like lubricant as additional or intermediate medium makesa comparatively less effort for sealing the housing necessary than inthe case of a oil which is capable of flowing more freely. For thedistribution of a paste-like lubricant so-called grease withdrawers,such as wipers, may be provided in order to transport the grease to thesurfaces to be greased, particularly the friction surfaces of thefrictional elements.

Upon using an oil as additional or intermediate medium amongst othersthe combinations steel/PA, steel/PEEK and POM/POM for the frictionsurfaces of the frictional elements, which friction surfaces cooperatewith each other, have been proven suitable.

According to an exemplary modification of the invention, at least one ofthe frictional elements, in particular the second frictional element, isadapted for embedding the additional or intermediate medium, e.g. due tothe use of a material in whose molecular structure the medium may beembedded or the use of a porous material in whose capillary structurethe medium may be embedded. Furthermore, at least one frictionalelement, in particular the second frictional element, may comprise areservoir for the additional or intermediate medium in its interior andmay be further provided with an open-pored capillary structure.

According to an exemplary further aspect of the invention, which,however, may be combined without further ado with the aspects of theinvention already stated, the two frictional elements may be elasticallybraced against one another so that their friction surfaces tend to bepressed against one another under the effect of the pre-tensioning,wherein one frictional element is mounted in such a way that it mayfollow up/be readjusted along the effective direction of thepre-tensioning force with respect to the other frictional element.

Due to the pre-tensioning force, which for example may be applied by anelastic element, by means of magnets or as well via the weight of thedisplaceable motor vehicle component or another vehicle component, thetwo frictional elements with their friction surfaces may be braisedagainst one another in a defined manner so that by using the differentmagnitudes of a sliding friction on the one hand and a static frictionon the other hand—depending on the materials used for the frictionsurfaces of the frictional elements—on the one hand a displacement ofsaid motor vehicle component as smooth as possible is permitted underthe influence of a sliding friction at the locking device and on theother hand the locking device secures the motor vehicle component indisplaced position as reliably as possible under the influence of astatic friction at the locking device. The respective material for thefriction surfaces of the two frictional elements, which frictionsurfaces cooperate with each other, is hence selected in such a way thatthe static friction between the friction surfaces of frictional elementsassociated to one another is substantially greater than the slidingfriction, in order to permit smooth running upon displacement of themotor vehicle component on the one hand and its reliable securing indisplaced position on the other hand. For this purpose—as statedabove—different material combinations for the cooperating frictionsurfaces of the locking device are provided which furthermore may becombined with a flowable additional or intermediate medium.

Since at least one frictional element is mounted in such a way that itmay be readjusted along the effective direction of the pre-tensioningforce with respect to the other friction element, it may be ensured,under the effect of the pre-tensioning force and by utilizing themounting of said frictional element through which mounting it may bereadjusted, that even after a long period of operation of the lockingdevice at a motor vehicle the desired friction conditions are alwaysmaintained because the friction surfaces of the two friction elementsare permanently pressed against each other with a defined pre-tensioningforce. Thereby, it is achieved, due to the capability of the onefriction element to may follow up along the effective direction of thepre-tensioning force, that the frictional elements may be brought intocontact with each other for generating desired friction forces.

Thereby, the one frictional element is in particular mounted moveablywith respect to the other frictional element along the effectivedirection of the pre-tensioning force in such a way that the otherfrictional element, under the effect of the pre-tensioning force, may beautomatically readjusted for generating mostly constant frictionconditions. In this respect, appropriate guiding means may be providedfor a defined guiding of the one frictional element along the effectivedirection of the pre-tensioning force.

For the generation of a pre-tensioning force, in particular of anelastic pre-tensioning force, an elastic element, such as in form of aspring such as a pressure or tension spring, flexible spring may serveaccording to an embodiment of the invention, which spring acts on atleast one of the two frictional elements. Examples for suitable springsare coil or disk springs as well as a rubbery-elastic element.

On the other hand, also magnetic forces for the generation of thepre-tensioning force may be used, for instance as one frictional elementat least particularly consists of a magnetic material, such as a magnetbound by a plastic, or is connected to an element of such material, andthe other frictional element at least partially consists of a materialwhich conducts the magnetic flux generated by the magnetic material oris connected to an element of such material.

Furthermore, also weights, for example the weight of the displaceablevehicle component itself, may be used for generating a pre-tensioningforce by means of which the two fictional elements are braised againstone another.

According to an exemplary modification of the invention, a housing isprovided in which the two frictional elements are arranged, wherein inparticular one of the two frictional elements may be arranged securelyon the housing and the other frictional element movably with respect tothe housing in such a way that the two frictional elements, upondisplacement of the associated motor vehicle component, are moveablerelative to each other and their friction surfaces thereby slide on oneanother. The housing may be arranged for example on the vehiclestructure, whereas the frictional element being moveable relative to thehousing is associated to the displaceable motor vehicle component. Thearrangement of one friction element in a manner that it is secured tothe housing thereby does not mean that the respective frictional elementhas to be necessarily arranged rigidly on the housing; in fact anarrangement with play or an elastic arrangement on the housing may beprovided for, for instance in order to permit a readjusting under theeffect of the pre-tensioning of the elastic element.

The second frictional element associated to the displaceable motorvehicle component may be coupled to said motor vehicle component via acoupling mechanism in such a way that it is turned about an axis upondisplacement of the motor vehicle component, or there may be providedfor a sliding movement of the second frictional element upon adisplacement of the motor vehicle component.

Further, there may be provided for that the friction surfaces of the twofrictional elements are inclined to the effective direction of thepre-tensioning force at an acute angle, so that, depending on said angle(i.e., a wedge angle), a force intensification occurs according to thewedge principle. In the case of a rotationally symmetrical design of thefrictional elements and the corresponding friction surfaces, inparticular with respect to an axis of rotation of the second frictionalelement, the friction surfaces associated to one another may be forexample in each case formed conically.

According to another exemplary embodiment, the friction surfaces of thetwo frictional elements, which friction surfaces cooperate with eachother, respectively extend perpendicular to the effective direction ofthe pre-tensioning force. The frictional elements then in each case forexample may be formed like a disk.

Using a wrapped spring for the second frictional element this one at thesame time also takes on the generation of the necessary pre-tensioningforce so that separate means for generating said pre-tensioning may beomitted.

According to an exemplary modification of the invention, severalfrictional elements may be provided for, which respectively cooperate inpairs via friction surfaces associated to one another. For this purpose,at least two pairs of friction surfaces may be also braised against oneanother along different, in particular opposing directions.

If the second frictional element associated to the displaceable motorvehicle component is coupled to the latter via a gearing, specifictransmission ratios, which may be pre-determined, may be establishedthereby, in particular for the increase of the motion speed of thesecond frictional element, and/or constructionally caused distancesbetween an output element of the displaceable motor vehicle componentand the second frictional element may be bridged, and/or a deflection ofthe direction of movement of the second frictional element may becarried out with respect to an activating displacement (e.g., adeflection movement) of the corresponding motor vehicle component.

According to a specific embodiment, the second frictional element isarranged on a shaft in a substantially torque-proof manner except for anoptionally necessary angular play, e.g. caused by an elastic mounting,i.e. in a manner so that it rotates with the shaft, which shaft, as apart of a coupling mechanism between the displaceable motor vehiclecomponent and the second frictional element, is turned upon displacementof the motor vehicle component, wherein the pre-tensioning force actsalong the direction of extent of the shaft and the second frictionalelement is movably mounted along that direction on the shaft, e.g. via akey and slot joint or another positive connection which indeed allowsfor a limited longitudinal movement of the second frictional elementalong the shaft, but not a free rotational movement of the frictionalelement about the shaft's axis.

In addition to the previously mentioned applications of the invention onmotor vehicle doors, front flaps or tailgates and other componentsassociated to the motor vehicle body, a locking device constructed inaccordance with the invention may be also used for securing a pluralityof other motor vehicle components such as a manually adjustable loadfloor or a manually adjustable blind which comprises an elasticallypre-stressed winding device and which shall be lockable in differentpositions unwound from the winding device. A further application relatesto the utilization of a locking device in accordance with the inventionas chocking device at electric drives, e.g. for window lifters, seatadjustments, door adjustments, load floor adjustments etc. Hereby, aself-locking design of such drives can be omitted, if the blocking offorces or torques induced on the output-side are taken on by a lockingdevice which for this purpose is provided for. Thereby, improvements onthe degree of efficiency of said drives may be achieved. In general, thelocking device in accordance with the invention may hence be applied onany motor vehicle components which are displaceable through movement andwhich shall be secured in a specific displaced position.

Consequently, the structural assembly of the motor vehicle with respectto which the motor vehicle component is to be displaced, or thestructural assembly of the motor vehicle with respect to which a firstfrictional element, not being moveable together with the displaceablemotor vehicle component, is to be secured, has not necessarily to be acomponent of the motor vehicle body. In fact, a basis, e.g. in the formof a housing, may generally serve for this purpose at which basis thefirst frictional element of the locking device may be directly orindirectly via further elements arranged and with respect to which thesecond frictional element is moveable in such a way that the secondfrictional element is moved with respect to the first frictional elementupon a displacement of the motor vehicle component associated to thelocking device.

An arrangement of the first frictional element at the structure therebythus not necessarily mean that said frictional element has to be rigidlyfixed at the respective structural assembly of the motor vehicle. Infact, a resilient mounting or a mounting, which is moveable along thepre-tensioning of an elastic element in a limited manner, can forexample be provided for.

The dimensioning, i.e. the selected size of the friction surfaces of thetwo frictional elements, of a possible wedge angle of the frictionsurfaces and of the pre-tensioning force which is exerted on the secondfrictional element, as well as the selection of the material of thecooperating pairs of friction surfaces and of the flowable intermediatemedium is carried out in dependence on the technical requirement in eachindividual case, i.e. for instance in dependence on hydrodynamicconditions as well as feasible surface pressures and wear parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention will become apparentupon the description of the following exemplary embodiments on the basisof the figures.

FIG. 1 a shows a first exemplary embodiment of a locking device for amotor vehicle door in cross-section.

FIG. 1 b shows a first embodiment of a frictional element for thelocking device from FIG. 1 a in perspective view.

FIG. 1 c shows a second embodiment of a frictional element for thelocking device from FIG. 1 a in perspective view.

FIG. 2 shows a second exemplary embodiment of a locking device for amotor vehicle door.

FIG. 3 shows a third exemplary embodiment of a locking device for amotor vehicle door.

FIG. 4 shows a fourth exemplary embodiment of a locking device for amotor vehicle door.

FIG. 5 shows a fifth exemplary embodiment of a locking device for amotor vehicle door.

FIG. 6 a shows a variant for the design of a positive fitting region ata frictional element of the locking device via which the frictionalelement may be brought in torque-proof and longitudinal moveableengagement with a shaft.

FIG. 6 b shows a variant for the design of a positive fitting region ata frictional element of the locking device via which the frictionalelement may be brought in torque-proof and longitudinal moveableengagement with a shaft.

FIG. 6 c shows a variant for the design of a positive fitting region ata frictional element of the locking device via which the frictionalelement may be brought in torque-proof and longitudinal moveableengagement with a shaft.

FIG. 6 d shows a variant for the design of a positive fitting region ata frictional element of the locking device via which the frictionalelement may be brought in torque-proof and longitudinal moveableengagement with a shaft.

FIG. 7 a shows a schematic representation of a possible positiveconnection between a frictional element and a shaft of the lockingdevice on the basis of the variant from FIG. 6 a.

FIG. 7 b shows a schematic representation of a possible positiveconnection between a frictional element and a shaft of the lockingdevice on the basis of the variant from FIG. 6 a.

FIG. 8 a shows a perspective view of a lateral vehicle structure of amotor vehicle with an opened vehicle door.

FIG. 8 b shows a perspective view of a rear side of a motor vehicle withan opened tailgate.

DETAILED DESCRIPTION

FIG. 8 a shows a detail of a lateral vehicle structure (body K) of amotor vehicle which, together with a roof section D of the motorvehicle, defines and encloses a door opening O trough which a passengermay enter the interior of the motor vehicle. For closing the dooropening O, a displaceable or deflectable motor vehicle component in theform of a hinged side door S is provided for, which in FIG. 8 a isdepicted in a partially opened position. A hinging of a side door S of amotor vehicle away from the vehicle structure K into a merely partiallyopened position is regularly carried out for example then when anothervehicle is parked next to the motor vehicle so that the side door S cannot be opened as wide as liked without colliding with the other vehicle.It is then important that the side door S is secured in the partiallyopened position in such a way that it is not further opened by a gust ofwind or an unintended contact of a pedestrian, since it hereby couldcollide with an adjoining other vehicle. For this purpose, so-calledlocking devices are provided for by means of which a side door S may besecured in a partially opened position.

It is an object to design such a locking device in such a way that it onthe one hand allows for a reliable securing of a motor vehicle door in apartially opened position, but at the same time does not interfere witha desired smooth movability of the vehicle door upon opening andclosing. Different exemplary embodiments of locking devices by meanswhich this object may be achieved will be described in the following onthe basis of the FIGS. 1 a to 5.

Previously it shall be pointed out on the basis of FIG. 8 b that lockingdevices of the mentioned type may not only be provided at side doors ofa motor vehicle, but for example as well at a rear door or tailgate Hprovided at a rear side R of motor vehicle and serving for closing atrunk compartment L. Further possible fields of applications are luggagecompartment flaps, motor flaps, sliding doors, adjustable loadfloorings, blinds or other vehicle components which are displaceable(i.e., deflectable) relative to a structural assembly of a motorvehicle. In the following it will be respectively spoken of deflectablemotor vehicle components in general, wherein in particular pivotable orhinged but also slidable motor vehicle components shall be comprised.

FIG. 1 a shows in a cross-section a first exemplary embodiment of alocking device by means of which a deflectable motor vehicle component,such as a side door according to FIG. 8 a or a rear door according toFIG. 8 b or a sliding door, may be secured in partially deflectedposition.

The locking device comprises a housing 5 with a housing's bottom part 51and a housing's top part 52 which are fixed to one another by means ofsuitable fixing means, e.g. in the form of screws or rivets. In thehousing 5 two friction elements 1, 2 are arranged which may be broughtinto engagement with each other via friction surfaces 10, 20 facing eachother, in order to continuously secure a deflectable motor vehiclecomponent in a partially deflected position due to the stiction (staticfriction) being effective thereby.

The first friction element 1 is formed by a section of the inner wall ofthe housing 5, to be precise a section of the inner wall of thehousing's bottom part 51, which is designed rotation-symmetrically withrespect to a housing's axis A and which defines or forms a frictionsurface 10 of the first frictional element, the friction surface 10conically tapering towards the bottom of the housing of the housing'sbottom part 51. Thus, the first frictional element is constructed in amanner fixed to the housing by forming its friction surface 10, which isrotation-symmetric with respect to the housing's axis A and tapersconically, as an integral part of an inner side wall of the housing 5,which side wall is annularly circumferential. Alternatively, a firstfrictional element fixed to the housing may be for example also realizedby fixing a frictional element, being separate of the inner wall of thehousing, in the interior of the housing.

The disk-shaped second friction element 2 is mounted on a shaft 3 in atorque-proof manner, which shaft at its two ends 31, 32 is respectivelymounted rotatably in an associated bearing 53 and 54 of the housing 5and whose pivot axis A coincides with the housing's axis with respect towhich the first frictional element 1 is formed rotational-symmetrically.The second frictional element 2 is also designed substantiallyrotational-symmetrically with respect to said axis A (except for astructuring of its friction surface) and tapers—as well as the firstfrictional element 1—towards the bottom of the housing being provided atthe housing's bottom part 51. Hereby, the second friction element 2defines a conic friction surface 20 at its outer circumference whichconic friction surface lies opposite to the conic friction surface 10 ofthe first friction element 1 and may be brought into frictionalengagement with the latter.

In order to bring the friction surfaces 10, 20 of the two frictionalelements 1, 2 into frictional engagement with each other, an elasticelement 4 in the form of a spring, to be precise of a coil springdesigned as a pressure spring, is provided, which encompasses the shaft3 and which is supported on the one hand on a widened end section 32 ofthe shaft 3 and on the other hand on the second frictional element,namely in such a way that it tends to brace the second frictionalelement 2 against the first frictional element 1 and hereby bring thetwo friction surfaces 10, 20 into engagement with each other. Expressedin other words, the effective direction R of the forces applied by thepre-tensioned, elastic element 4 or the respective pre-tensioning issuch that it extends along the shaft 3 or its axis A, respectively, andbraces the second frictional element 2 along said direction R againstthe first frictional element 1.

In order to permit an axial movability of the second frictional element,which is mounted on the shaft 3 in such a way that it turns with theshaft, so that this one may be brought into engagement with the frictionsurface 10 of the first frictional element 1 in a defined manner alongthe effective direction R of the pre-tensioning of the elastic element4, the torque-proof mounting of the second frictional element at theassociated shaft 3 is carried out by means of positive fitting regions25, 35 of the frictional element 2 and the shaft 3, which positivefitting regions engage into each other and allow for an axial movabilityof the second frictional element 2 along the axis A of the shaft 3 andthus also the housing's axis coinciding therewith. Precisely, thepositive fitting regions 25, 35 here exemplarily form a key and slotjoint comprising a groove 25, which is provided at the second frictionalelement 2 and extends along the shaft's axis A, and comprising anassociated spring 35 in the form of a projection, which spring protrudesoutwardly from the shaft 3 into the groove 25.

The positive fitting region 35 in the form of a spring, which positivefitting region protrudes outwardly from the shaft 3, engages into theassociated positive fitting region 25 in the form of a groove of thesecond frictional element 2 in such a way that the second frictionalelement 2 is mounted on the shaft 3 in a substantially torque-proofmanner, except for an angular play optionally provided for, but may bemoved—under the effect of the pre-tensioning of the elastic element4—along the axis A in a limited way, wherein the maximum possible extendof the movement is limited in that the second frictional element withits friction surface 20, under the effect of the pre-tensioning of theelastic element 4, is pushed against the associated friction surface 10of the first frictional element 1.

Due to its axially movable mounting, the second frictional element 2 iscapable, under the effect of the pre-tensioning of the elastic element4, to be automatically readjusted/to follow up in such a way thatit—even after a long period of operation of the locking device and thewear related therewith—always engages the associated friction surface 10of the first frictional element 1 in a defined manner. The readjustmentis thereby carried out automatically under the effect of thepre-tensioning of the elastic element 4 and by utilizing the axialmovability of the second frictional element 2 along the shaft 3.

The material for the friction surfaces 10, 20 of the two frictionalelements 1, 2 has to be selected such that the two friction surfaces 10,20, when they engage each other under the effect of the pre-tensioningof the elastic element 4, establish a sufficiently strong staticfriction in order to secure a motor vehicle component, which ispartially deflected with respect to the vehicle structure, in itsdeflected position by means of the locking device. Suitable materialcombinations for the two friction surfaces 10, 20 have been alreadymentioned above. In the present case, it may be for example assumed thatthe two friction surfaces 10, 20 are respectively made up of POM(polyoxymethylene).

In addition to a reliable securing of a deflected motor vehiclecomponent, the locking brake shall furthermore permit a deflecting ofthe respective motor vehicle component as smooth as possible; i.e. thefrictional forces being effective between the two friction surfaces 10,20 of the frictional elements 1, 2 shall be as small as possible upon arelative movement of the two frictional surfaces 10, 20 relative to eachother. Expressed with other words, the sliding friction being effectivebetween the two friction surfaces 10, 20 upon a relative movement shallbe significantly less, preferably a less many times over, than thestatic friction which is effective between the friction surfaces 10, 20when the second frictional element 2 is braced against the firstfrictional element 1 by means of the elastic element 4 in a position ofrest.

The movement of the second frictional element upon a deflection of anassociated motor vehicle component which is to be secured by means ofthe locking brake, such as a side door or rear door of a motor vehicle,is thereby activated in that the shaft 3, on which the second frictionalelement 2 is mounted in a torque-proof manner, is coupled with saiddeflectable motor vehicle component, namely in such a way that adeflection of said motor vehicle component, i.e. for instance a vehicledoor, is transformed into a rotational movement of the shaft 3 aroundits axis A. For this purpose, the shaft 3 on the one hand may affectdirectly at a swivel axis around which a deflectable motor vehiclecomponent is swivelled, or a gearing may be installed before the shaft 3via which a deflection of the respective motor vehicle component istransformed into a rotational movement of the shaft. Such a gearing thancan for example cause a specific transformation for an increased speedof the second frictional element or also a change of direction, forinstance in order to orient the shaft 3 in a certain direction.

As a result, the second frictional element 2 is to be coupled via thecorresponding shaft 3 to an associated deflectable motor vehiclecomponent, such as a vehicle door, in such a way that a deflection ofsaid motor vehicle component results in a rotational movement of theshaft 3.

The other first frictional element 1 has than to be fixed with respectto the vehicle structure in such a way that it is not entrained upon adeflection of the motor vehicle component to be secured. This mayparticularly be achieved in that the housing 5, at who's inner wall thefirst frictional element 1 with its friction surface 10 is formed, isarranged on the structure at the vehicle, for example at a frame work ofa vehicle door associated to the locking device.

Thus, a deflection movement of the deflectable motor vehicle componentassociated to the locking device in consequence results in that thesecond frictional element 2 is twisted around the axis A with respect tothe first friction element 1 by means of the shaft 3, wherein the twoconic friction surfaces 10, 20 slide on one another. Now it is an objectto limit the sliding frictional forces being effective thereby—at thesame time ensuring static frictional forces as strong as possible—insuch a way that no too strong friction forces counteract a deflection ofsaid motor vehicle component. On the one hand, an appropriate selectionof the materials used for two cooperating friction surfaces 10, 20 maycontribute to this, in particular by using such material pairings atwhich the static friction is substantially greater, in particulargreater many times over, than the sliding friction.

Alternatively or additionally, the use of a flowable additional orintermediate medium Z is in the present case provided for which is to bebrought between the friction surfaces 10, 20 of the two frictionalelements 1, 2, which friction surfaces face each other, during amovement of the second frictional element 20 relative to the firstfrictional element 1 and reduces the acting friction forces. As alubricant for the reduction of the friction forces, a suitable oil, suchas flour silicone basis oil with ester additives may be used, namelyindeed in combination with friction surfaces 10, 20 which arerespectively made up of POM.

The additional or intermediate medium Z in the form of a lubricant, i.e.composed of a flowable material, is provided in the housing's bottompart, namely with such a filling level that it reaches at least to thebottom side of the second frictional element 2, which bottom side facesthe bottom of the housing.

In order that a sufficient portion of the flowable additional orintermediate medium Z may get between the friction surfaces 10, 20 ofthe frictional elements 1, 2 during a relative movement, i.e. a rotarymovement, of the second frictional element 2 with respect to the firstfrictional element 1 and the sliding friction thereby is accordinglyreduced, guiding channels 21 are provided along the friction surface 20of the second frictional element 2, cf. FIGS. 1 b and 1 c, along whichguiding channels the additional or intermediate medium may rise during arotational movement of the second frictional element 2 so that it getsbetween the two friction surfaces 10, 20.

In the state of rest of the second frictional element 2, i.e. when forinstance a deflected motor vehicle component shall be secured indeflected position by means of the locking device, the additional orintermediate medium Z is pressed out from the area between the frictionsurfaces 10, 20, bearing against one another, under the effect of thepre-tensioning force of the elastic element 4 so that the staticfriction is not affected.

According to the embodiment of the second frictional element shown inFIG. 1 b, the channels 21 are formed as recesses (e.g., grooves orflutes) in the friction surface 20 of the second frictional element 2,which recesses substantially extend along the shaft 3 or its axis A,respectively, but which thereby—in accordance with the inclination ofthe friction surface 20—are inclined to said direction.

At the variant shown in FIG. 1 c, the friction surface 20 of the secondfriction element 2 consists of a plurality of spherical portions whichare arranged one after the other along the circumferential direction ofthe disk-shaped frictional element and which for example respectivelyrepresent a segment of a circle whose radius r_(b) is smaller than theradius r_(o) of the circular path along which the spherical portions arearranged one after the other. Thereby, guiding channels 21 for theflowable additional or intermediate medium Z are respectively formed atthe places at which the spherical portions adjoin.

The type and amount of the additional medium Z to be provided for is tobe selected advantageously in such a way that, on the one hand, thesecond frictional element 2 preferably does not swim on it and, on theother hand, the additional medium Z may be urged, as described above,out of the area of the friction surfaces of the friction elements 1, 2,which friction surfaces are associated to each other, in order to permitstatic friction in the state of rest.

Altogether, the FIGS. 1 a to 1 c hence result in the following: If thedeflection movement ends which caused the displacement of a motorvehicle component associated to the locking device, such a vehicle door,the shaft 3 does not rotate further and the second frictional element 2lies stationary opposite to the first frictional element 1, the mutualfriction surfaces 10, 20 bearing against one another. Under the effectof the pre-tensioning force generated by the elastic element 4 theintermediate medium Z being present between the two friction surfaces10, 20 is then pushed away at least at the places at which the frictionsurfaces 10, 20 directly bear against one another. After a shorttransition period, which is necessary for pushing the intermediatemedium Z away, the increased dry static friction between the twofriction surfaces 10, 20 then sets in.

If the respective motor vehicle component is afterwards moved again, forexample, in order to deflect it further or in order to swivel it back toits initial position, the static friction between the friction surfaces10, 20 of the locking device first of all has to be overcome therefor.Once the second frictional element with its friction surface 20 is thenagain moved with respect to the first frictional element 1 and itsfriction surface 10, i.e. is turned, it is ensured by means of theguiding channels 21, which upon a rotary movement of the secondfrictional element bit by bit pass over all regions of the frictionsurface 10 of the first frictional element 1, that the friction surface10 of the friction element 1 is continuously wetted with intermediatemedium Z, over which the friction surface 20 of the second frictionalelement 2 then may slide with reduced sliding friction.

FIG. 2 shows an alternative of the embodiment from FIG. 1 a according towhich the housing 5 in its mounting position, i.e. in the position inwhich it is to be mounted as intended in a motor vehicle, is orientatedin such a way that the shaft 3 and its axis A extend horizontally,whereas the shaft 3 and its axis A at the embodiment shown in FIG. 1 aextend vertically in the mounted position, i.e. for instance along thevertical axis of a motor vehicle.

In the case of the arrangement from FIG. 2, the additional orintermediate medium Z thus accumulates not only in the housing's bottompart 51 (as it is possible at the arrangement from FIG. 1 a), so thathere a sealing of the connecting area between the two housing parts 51,52 is necessary. For this purpose, the two housing parts 51, 52 bearagainst on one another via in each case one fixing flange 51 a, 52 a,which outwardly protrudes and e.g. is annularly circumferential, namelywith the interposition of a seal D between the two fixing flanges 51 a,52 a.

FIG. 3 shows a further alternative of the arrangement from FIG. 1 aaccording to which two pairs of friction surfaces 10, 20 and 110, 120are provided along which in each case a first frictional element 1 or101 being fixed to the housing and a second frictional element 2 or 102being twistable thereto cooperate. The two frictional elements 1, 101being fixed to the housing are respectively formed at the inner wall ofthe housing 5, and indeed, opposing each other, the one first frictionalelement 1 at the housing's bottom part 51 and the other first frictionalelement 101 at the housing's top part 52. The frictional element 1formed at the inner wall of the housing's bottom part 51 thereby tapersconically towards the bottom of the housing and the frictional element101 formed at the inner wall of the housing's top part 52 tapersconically towards the upper top surface of the housing's top part 52.The two frictional elements 1, 101 being fixed to the housing are henceformed substantially symmetrical with respect to a plane runningperpendicular to the axis A of the shaft 3.

In the housing 5, which is formed by the two housing parts 51, 52 andwhose housing parts 51, 52 are connected to each other via fixingflanges 51 a, 52 a protruding outwardly, are further received two secondfrictional elements 2, 102 which are respectively associated to one ofthe first frictional elements 1, 101 or its friction surface 10, 110formed at the inner wall of the housing 5, respectively. Thereby, thesecond frictional element 2 associated to the first frictional element 1of the housing's bottom part is secured in a torque-proof manner at theshaft 3 projecting into the housing 5, as well as in the case of FIGS. 1a and 2, via key and slot joint V, which is schematically indicated inFIG. 3, and thereby at the same time is axially movable along the shaft3 or its axis A, respectively.

The other second frictional element 102 which faces the first frictionalelement 101 of the housing's top part, in contrast thereto, is fixedly,i.e. for instance integrally, connected to the shaft 3. Both secondfrictional elements 2, 102 respectively have a conically taperedfriction surface 20 or 120 at the outer circumference, which frictionsurface may be brought into frictional engagement with the respectivelyassociated friction surface 10, 110 of the corresponding firstfrictional element 1 or 101. For this purpose, at least one elasticelement in the form of a pressure spring is arranged the two frictionalelements 2, 102 which elastic element tends to push the two secondfrictional elements 2, 102 in opposing directions R1, R2 along the shaft3 or its axis A, respectively, apart from one another in such a way thateach of the two second frictional elements 2, 102 with its frictionsurface 20 or 120 is pressed against the friction surface 10 or 110 ofthe associated first frictional element 1, 101.

An axial movability of the second frictional element 2 of the housing'sbottom part is thereby ensured via its longitudinally movable mountingat the shaft 3. The other second frictional element 102 of the housing'stop part, in contrast thereto, is rigidly connected to the shaft 3,wherein a movability along the shaft's axis A here is e.g. permitted bymounting the shaft 3 in total movably in axial direction at the housing5. If necessary, the friction surface pairing 110, 120 of the housing'stop part may also be permanently engaged.

By the way, the individual pairs of friction surfaces 10, 20 or 110,120, as regards their design, are identical to the pair of frictionsurfaces 1, 2 as illustrated on the basis of FIG. 1 a so that it isreferred to the explanations for FIGS. 1 a to 1 c for further details.

Due to the forming of two pairs of friction surfaces 10, 20; 110, 120 atthe arrangement shown in FIG. 3 instead of merely one pair of frictionsurfaces 10, 20 at the arrangements shown in FIGS. 1 a and 2, acorresponding greater locking force, as sum of the static frictionforces being effective at the two pairs of friction surfaces 10, 20;110, 120, may be achieved with a locking device.

FIG. 4 shows an alternative of the embodiment from FIG. 1 with threefirst frictional elements 1 a, 1 b, 1 c fixed to the housing and twosecond frictional elements 2 a, 2 b arranged in a torque-proof manner atthe shaft 3, wherein the first and second frictional elements 1 a, 1 b,1 c; 2 a, 2 b are alternately arranged one after the other along theshaft 3 or its axis A, respectively. Not the outer circumferential facesof the disk-shaped frictional elements 1 a, 1 b, 1 c; 2 a, 2 b here dothereby serve as friction surfaces, but rather their top and bottomsides 10 a, 10 b, 10 c; 20 a, 20 b, so that there is a plurality offriction surface pairings 10 a, 20 a; 20 a, 10 b; 10 b, 20 b; 20 b, 10 cat which in each case a friction surface 10 a, 10 b, 10 c of a firstfrictional element 1 a, 1 b, 1 c, being fixed to the housing, bearsagainst a friction surface 20 a, 20 b of a second frictional element 2a, 2 b, being mounted at the shaft 3, in such way that it turns with theshaft, namely under the effect of the pre-tensioning from at least oneelastic element 4 in the form of a pressure spring which at the one handis supported at the housing 5, in particular at its top surface, and onthe other hand at a frictional element 1 c, which is fixed to thehousing but is movable in axial direction.

Thereby, only one (1 a) of the frictional elements 1 a, 1 b, 1 c beingfixed to the housing here is formed as a part of an inner housing wall,namely of the bottom of the housing, whereas the two other frictionalelements 1 b, 1 c being fixed to the housing are in each case movablyhoused along the shaft 3 or its axis A, respectively, in a side wall ofthe housing through a key and slot joint V.

One frictional element 2 a of the two second frictional elements 2 a, 2b is rigidly, in particular integrally, connected to the shaft 3 and theother frictional element 2 b is arranged axially and longitudinallymovably (however, at the same time in a manner so that it turns with theshaft or in a torque-proof manner) at the shaft 3 via a key and slotjoint V. A longitudinal movability of the second frictional element 2 abeing integrally formed on the shaft 3 may thereby result from mountingthe shaft 3 in total in a limited manner longitudinally movably in thehousing 5.

By bracing the outmost upper first frictional element 1 c, which facesaway from the bottom of the housing, in axial direction by means of atleast one elastic element 4, taking advantage of the axial movability ofthe upper first frictional element 1 c, which is mounted at the housing5 via a key and slot joint, the pairs of friction surfaces 10 a, 20 a;20 a, 10 b; 10 b, 20 b; 20 b, 10 c are pushed against one another underthe effect of the elastic pre-tensioning force in such a way that adesired static frictional force occurs which serves for securing adeflected motor vehicle component in deflected position.

Since here the force intensification due to the wedge effect, as it ispresent in the embodiments of FIGS. 1 a, 2 and 3, is omitted, asufficiently strong locking force in the arrangement shown in FIG. 4 isachieved in that here four pairs of friction surfaces cooperate.

Just one first frictional element 1 a with its friction surface 10 a isthereby formed immovably in axial direction at the housing 5, to beprecise on the bottom of the housing. All the other frictional elements1 b, 1 c and 2 a, 2 b are mounted movably in axial direction, whereinthe two first frictional elements 1 b, 1 c are mounted longitudinallymovably at a side wall of the housing's bottom part 51 via in each caseone key and slot joint V and the two second frictional elements 2 a, 2 bare longitudinally movably accommodated at the shaft 3 via in each caseone key and slot joint V.

FIG. 5 shows, in a modification of the embodiment from FIG. 4, adoubling of the arrangement from FIG. 4, i.e. there is respectivelyprovided an arrangement consisting of first and second frictionalelements 1 a, 1 b, 1 c; 2 a, 2 b or 101 a, 101 b, 101 c; 102 a, 102 b ata lower housing part 51 as well as at an upper housing part 52, whereinthe two arrangements of frictional elements will be braced by means ofelastic elements 4 which, if viewed in axial direction, lie between thetwo arrangements and brace the two arrangements in directions R1 and R2,opposing each other, in such a way that their friction surfaces arepressed against one another respectively generating a suitably strongfriction force, in particular a static friction of the shaft 3 rests anddoes not turn.

Both in the case of the arrangement from FIG. 4 and in the case of thearrangement from FIG. 5 an additional or intermediate medium Z isrespectively arranged in the housing 5 which additional or intermediatemedium may be guided between the friction surfaces 10 a, 10 b, 10 c; 20a, 20 b and 110 a, 110 b, 110 c; 120 a, 120 b of the frictionalelements, which friction surfaces bear against each other, throughsuitable channels during a rotation of the second frictional elements 2a, 2 b or 2 a, 2 b; 102 a, 102 b in order to reduce the slidingfriction, and which additional or intermediate medium is pressed out ofthe area between the friction surfaces facing each other when the shaftsrests and thus the second frictional elements 2 a, 2 b or 2 a, 2 b; 102a, 102 b rest, in order to achieve a maximum static friction and thus alocking force of the locking device as strong as possible.

In FIGS. 6 a to 6 d differently designed positive fitting regions at asecond friction element 2 are shown in cross-section via which therespective disk-shaped second frictional element 2 may be arranged atthe shaft 3 in a torque-proof manner but at the same time longitudinallymovably, cf. FIGS. 1 a to 5.

FIG. 6 a schematically shows once more the design of a positive fittingregion 25 known from FIGS. 1 a to 1 c, in particular FIGS. 1 b and 1 c,as a groove extending along the shaft 3 or its axis A, respectively.

According to FIG. 6 b, a plurality of such positive fitting regions 25,in the present case for example four positive fitting regions, arearranged one after the other at the inner circumference of thedisk-shaped frictional element along the circumferential direction.

According to FIG. 6 c, the positive fitting regions 26 being arrangedone after the other at the circumference of the disk-shaped frictionalelement 2 along the circumferential direction in each case have, incross-section, a rounded shape and, according to FIG. 6 d, the positivefitting regions 27 are respectively provided, in cross-section, with atriangular shape.

FIG. 7 a shows that into a positive fitting region 25 in the form of agroove at the inner circumference of a frictional element 2 a positivefitting region 35 in the form of a spring on the shaft, which springprotrudes from the shaft 3 or, to be precise, from its outer surface andengages into the groove 25, may project.

Likewise, an opposite further groove 35′ at the outer surface of theshaft 3 may also be associated to a positive fitting region 25 at theinner surface of the second frictional element 2 which positive fittingregion is formed by groove, wherein the connection is then establishedby a closing member E which is inserted in a hollow space formed by thetwo grooves 25, 35′.

FIG. 7 b clearly depicts how a connection which is torque-proof or atleast turns with the shaft and which permits a movability of thefrictional element 2 in axial direction a may be established with a keyand slot joint being formed by a groove-type positive fitting region 25at the second frictional element 2 and a spring 35 protruding from theshaft 3, by the groove 25 having a greater extent in axial direction athan the spring 35 to be mounted therein, wherein, however, at the sametime the spring 35, perpendicular to the axial direction a, is installedsubstantially immovably, except for an angular play optionally providedfor in the associated groove 25.

Naturally, the other way round, at least one groove at the shaft 3 andat least one corresponding spring at the second frictional element 2 mayalso be provided for, like it is e.g. schematically indicated above inFIGS. 2 to 5.

The invention claimed is:
 1. A locking device for securing a motorvehicle component which is displaceable relative to a motor vehiclestructure and which is securable by the locking device within adisplacement range in a position of rest, the locking device comprising:a first frictional element; and a second frictional element which ismovable relative to the first frictional element and thereby slideablewith a friction surface along a friction surface of the first frictionalelement under sliding friction conditions and wherein, in the positionof rest of the motor vehicle component, the friction surface of thefirst frictional element bears against the friction surface of thesecond frictional element under static friction conditions, wherein thefirst frictional element and the second frictional element arepre-tensioned against one another in such a way that they tend to abutone another with their friction surfaces, and at least one of the firstfrictional element and the second frictional element is mounted in sucha way that it is adjustable along an effective direction ofpre-tensioning with respect to the other of the first frictional elementand the second frictional element, wherein a flowable additional mediumis provided which is configured to be brought, upon a relative movementof the frictional elements, between the friction surface of the firstfrictional element and the friction surface of the second frictionalelement, wherein the first frictional element comprises an inner wallfacing the second frictional element, wherein the inner wall of thefirst frictional element is conically shaped and defines the frictionsurface of the first frictional element, and wherein the secondfrictional element is rotatable with respect to the first frictionalelement about an axis of rotation and comprises an outer wall facing thefirst frictional element and extending about the axis of rotation,wherein the outer wall is conically shaped and defines the frictionsurface of the second frictional element, the second frictional elementhaving an upper circumferential edge bounding the outer wall at an upperside of the second frictional element and at a lower circumferentialedge bounding the outer wall towards a lower side of the secondfrictional element, wherein at least one guide channel is provided atone of the first frictional element and the second frictional element,the at least one guide channel extending substantially along theeffective direction of pre-tensioning, and being inclined at an angle toextend substantially parallel to the friction surface of the one of thefirst frictional element and the second frictional element, wherein theat least one guide channel extends longitudinally between the uppercircumferential edge and the lower circumferential edge of the secondfrictional element and is open at the upper side of the secondfrictional element and at the lower side of the second frictionalelement.
 2. The locking device according to claim 1, wherein the atleast one guide channel is configured to bring the flowable additionalmedium between the friction surface of the first frictional element andthe friction surface of the second frictional element.
 3. The lockingdevice according to claim 1, wherein at least one of the firstfrictional element and the second frictional element is configured toaccommodate the flowable additional medium.
 4. The locking deviceaccording to claim 3, wherein at least one of the first frictionalelement and the second frictional element is composed of a materialconfigured to accommodate in its molecular structure the flowableadditional medium or is composed of a porous material configured toaccommodate in its capillary structure the flowable additional medium.5. The locking device according to claim 3, wherein at least one offirst frictional element and the second frictional element comprises areservoir for the flowable additional medium.
 6. The locking deviceaccording to claim 1, further comprising a device constituted toincrease the static friction being effective, due to the pre-tensioningof the frictional elements, between the friction surface of the firstfrictional element and the friction surface of the second frictionalelement bearing against one another.
 7. The locking device according toclaim 1, wherein the second frictional element is coupled to thedisplaceable motor vehicle component in such a way that the secondfrictional element is twisted or moved relative to the first frictionalelement upon a displacement of the motor vehicle component.
 8. Thelocking device according to claim 1, wherein the second frictionalelement is configured to be coupled to the displaceable motor vehiclecomponent via a coupling mechanism, wherein the coupling mechanismcomprises a shaft to which the second frictional element is connected soas to rotate with the shaft and which is configured to be operativelyconnected to the motor vehicle component, wherein the second frictionalelement is connected to the shaft in a positive locking manner such thatthe second frictional element is mounted, with respect to the shaft, soas to rotate with the shaft and at the same time to be axially movable.9. The locking device according to claim 8, wherein, for the connectionof the second frictional element to the shaft, a key-and-slot joint, atooth engagement or other positive fitting regions engaging one anotherare provided.
 10. The locking device according to claim 1, wherein thefriction surface of the first frictional element and the frictionsurface of the second frictional element are composed of materials whichare selected so that the sliding friction upon a relative movement ofthe first frictional element and the second frictional element issubstantively smaller than the static friction upon stationary bearingof the first frictional element and the second frictional element oneach other.
 11. The locking device according to claim 1, wherein a ratioof static friction to sliding friction is equal to or greater than 3.12. A locking device for securing a motor vehicle component which isdisplaceable relative to a motor vehicle structure and which issecurable by the locking device within a displacement range in aposition of rest reached by displacement of the locking device,comprising: a first frictional element; and a second frictional elementwhich is movable relative to the first frictional element and therebyslideable with a friction surface along a friction surface of the firstfrictional element under sliding friction conditions and wherein, in theposition of rest of the motor vehicle component, the friction surface ofthe first frictional element bears against the friction surface of thesecond frictional element under static friction conditions, wherein thefirst frictional element and the second frictional element arepre-tensioned against one another in such a way that they tend to abutone another with their friction surfaces, and at least one of the firstfrictional element and the second frictional element is mounted in sucha way that it is adjustable along an effective direction ofpre-tensioning with respect to the other of the first frictional elementand the second frictional element, wherein the first frictional elementcomprises an inner wall facing the second frictional element, whereinthe inner wall of the first frictional element is conically shaped anddefines the friction surface of the first frictional element, whereinthe second frictional element is rotatable with respect to the firstfrictional element about an axis of rotation and comprises an outer wallfacing the first frictional element and extending about the axis ofrotation, wherein the outer wall comprises a generally conical shape anddefines the friction surface of the second frictional element, thesecond frictional element having an upper circumferential edge boundingthe outer wall at an upper side of the second frictional element and alower circumferential edge bounding the outer wall towards a lower sideof the second frictional element, wherein the friction surface of thesecond frictional element comprises spherically shaped sectionsadjoining each other along a circle extending circumferentially aboutthe axis of rotation so that the second frictional element is configuredto be brought into engagement with the friction surface of the firstfrictional element merely via a portion of its friction surface, eachspherical section having a radius of curvature smaller than the radiusof the circle along which the spherically shaped sections adjoin eachother, wherein at least one longitudinally extending guide channel isformed between adjoining spherical sections, extends longitudinallybetween the upper circumferential edge and the lower circumferentialedge of the second frictional element, and is open at the upper side ofthe second frictional element and at the lower side of the secondfrictional element.